Cellulosic fibers such as paper pulp, bagasse, insulation or fiber board materials, cotton and the like, are commonly subjected to a refining operation which consists of mechanically rubbing the fibers between sets of relatively rotating bar and groove elements. In a disk-type refiner, for example, these elements commonly consist of plates having annularly arranged bar and groove patterns defining their working surfaces, with the bars and grooves extending generally radially of an axis of the rotating element, or more often at an angle oblique to a radius to the center of the annular pattern, so that the stock can work its way from the center of the pattern to its outer periphery.
Disk-refiners are commonly manufactured in both single and twin disk types. In a single disk refiner, the working surface of the rotor comprises an annular refiner plate, or a set of segmental refiner plates, for cooperative working action with a complementary working surface on the stator, which also comprises an annular plate or a series of segmental plates forming an annulus. In a twin disk refiner, the rotor is provided with working surfaces on both sides. The working surfaces of the rotor cooperate with a pair of opposed complementary working surfaces on the stator, with these working surfaces being generally of the same type of construction as with a single disk refiner.
Paper pulp refiners as described, including the plug or cone type refiners, require the control of the position and axial spacing of the relatively rotating members for the purpose of controlling refiner load and for controlling the quality of the refined paper fiber product, among other reasons. A plug type refiner is shown in Staege et al., U.S. Pat. No. 2,666,368, while a control arrangement for a dual inlet disk type refiner is shown in Hayward U.S. Pat. No. 3,506,199.
Known refiners have included mechanical drive systems for moving one refining element closer or farther from the other along the axis of rotation of the rotor. It also is known to provide electrical or electronic controllers, such as that shown in Hayward, to control the axial spacing of the refining elements in response to motor load, changing voltage or power factors, or pulp quality. Reference may be had to Baxter U.S. Pat. No. 2,986,434, which shows a dual inlet radial disk type refiner and the reduction gearing through which the axial position of the stator and rotor elements may be accurately determined and maintained.
Mechanical refining is optimized when the gap between the refining elements of the stator and rotor is on the order of 0.001 inch to 0.010 inch (0.025 mm to 0.25 mm). The actual spacing of the stator and rotor plates is dependent upon numerous stack-up items in the assembly of the refiner. Due to typical manufacturing tolerances, the design misalignment can be as much as 0.045 inch (1.1 mm).
One drawback to known refining systems is that they make no provision for correcting errors in the trim, or angular orientation, of the refining elements relative to one another. Thus, when the stator plate is inclined relative to the rotor plate, for example, certain portions of the refining surface of the refining element mounted by the stator plate will be closer to the complementary surface of the refining element mounted by the rotor than other portions of the refining surface. This implies a variation in the width of the refining gap between the refining elements along the surfaces of the refining elements even when the average or overall refining gap is optimized.
Dodson-Edgars U.S. Pat. No. 4,820,980 shows an apparatus and method for measuring the gap, tram, deflection and wear of rotating grinding plates such as those found in mechanical refiners. In particular, Dodson-Edgars shows inductive sensors mounted in a recessed manner inset from the surface of a first grinding plate and located opposite recessed non-wear surfaces of a second grinding plate. The sensors are monitored by a microprocessor system, which processes signals from the sensors to determine gap, tram, deflection and wear. Dodson-Edgars teaches that plate tram may be controlled by angular displacement of the drive shaft which drives one of the rotating plates or by angular displacement of the other, stationary plate, but does not disclose any apparatus for carrying out such an adjustment.
Thus, there remains a need in the art for an improved mechanical refining system providing control, preferably automatic control, of the trim of the refining elements mounted by the stator and rotor relative to one another, as well as providing automatic control of the average or overall refining gap between the elements.